Kai Walter Zweiacker

Kai Walter Zweiacker
Empa - Swiss Federal Laboratories for Materials Science and Technology | Empa · Center for X-Ray Analytics

PhD

About

26
Publications
5,778
Reads
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513
Citations
Citations since 2016
19 Research Items
489 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120

Publications

Publications (26)
Article
Full-text available
Controlling the grain size of steels is an effective way for tailoring their mechanical properties, such as yield strength, impact toughness, and ductility. In this study, a new industrial thermomechanical treatment was applied to a low-alloyed TRIP-assisted bainitic steel 13MnSiCr7 to achieve a substantial microstructural refinement. In this way t...
Article
Full-text available
Laser powder bed fusion (L-PBF) of copper alloys with high copper content is difficult due to the high infrared reflectivity and thermal conductivity of these alloys. In this study a simple and scalable method for coating copper powder with tin and nickel is presented, and suggested as an alloying strategy for such alloys. The coated powders were p...
Article
The additive manufacturing (AM) of the γ` precipitation strengthened Ni-base superalloys still remains a challenge due to their susceptibility to micro-cracking. Post-processing, such as HIPing, has been shown to heal the micro-cracks but it remains desirable to prevent the micro-cracking from even occurring. Numerous studies highlighting potential...
Article
Microstructure formation of a hypo-eutectic Al-11Cu (atom percent) alloy during solidification after laser melting has been studied by transmission electron microscopy (TEM). The evolution of the solid-liquid-interface velocity, VSL, during the solidification process has been determined from direct observation by in-situ TEM. This enabled correlati...
Article
Full-text available
Laser beam-based deposition methods such as laser cladding or additive manufacturing of metals promises improved properties, performance, and reliability of the materials and therefore rely heavily on understanding the relationship between chemical composition, rapid solidification processing conditions, and resulting microstructural features. In t...
Article
Here we present measurements of surface tension and viscosity of the bulk glass-forming alloy Pd43Cu27Ni10P20 performed during containerless processing under reduced gravity. We applied the oscillating drop method in an electromagnetic levitation facility on board of parabolic flights. The measured viscosity exhibits a pronounced temperature depend...
Article
Full-text available
Here we present measurements of surface tension and viscosity of the bulk glass-forming alloy Pd_(43)Cu_(27)Ni_(10)P_(20) performed during containerless processing under reduced gravity. We applied the oscillating drop method in an electromagnetic levitation facility on board of parabolic flights. The measured viscosity exhibits a pronounced temper...
Article
The scanning X-ray nanodiffraction technique is used to reconstruct the three-dimensional distribution of lattice strain and Ge concentration in compositionally graded Si 1− x Ge x microcrystals grown epitaxially on Si pillars. The reconstructed crystal shape qualitatively agrees with scanning electron micrographs and the calculated three-dimension...
Article
Rapid solidification can produce metastable phases and unusual microstructure modifications in multi-component alloys during additive manufacturing or laser beam welding. Composition and phase mapping by transmission electron microscopy have been used here to characterize the morphologically distinct zones developing in hypoeutectic Al-4 at.% Cu al...
Article
In this study, we investigate the effect of thermo-mechanical processing (TMP) on the evolution of low coincident site lattice (CSL) grain boundaries (3 ≤ Σ ≤ 27) and thence on the precipitation behavior of carbides at various types of grain boundaries in Alloy 600. Detailed analysis of the microstructure using Electron Back-scattered Diffraction (...
Article
Composition and Crystal Orientation Mapping of nano-scale multi-phase Rapid Solidification Microstructures in hypo-eutectic Al-Cu Alloy Thin Films - Volume 23 Issue S1 - Jörg M.K. Wiezorek, Can Liu, Sahar Farjami, Kai W. Zweiacker, Joseph T. Mckeown, Geoffrey H. Campbell
Article
Atom Probe Tomography and analytical Scanning Transmission Electron Microscopy of Rapid Solidification Microstructures in Al-Cu Alloy Thin Films - Volume 23 Issue S1 - Jorg M.K. Wiezorek, Kai W. Zweiacker, Can Liu, Isabelle Martin, Ty. J. Prosa, David J. Larson
Conference Paper
Full-text available
Non-destructive testing of parts, after flight, could substantially reduce the costs of space travel. The reusability of equipment had already been planned in 1992 when the EURECA satellite was first launched, which was retrieved 11 months later. A unique multi-scale analysis, using various X-ray systems at Empa, evaluates the influence of launchin...
Article
In situ investigations of rapid solidification in polycrystalline Al thin films were conducted using nano-scale spatio-temporal resolution dynamic transmission electron microscopy. Differences in crystal growth rates and asymmetries in melt pool development were observed as the heat extrac- tion geometry was varied by controlling the proximity of t...
Article
div class="title"> Nano-Scale Spatio-Temporal Resolution in situ TEM and Numerical Modeling of Rapid Solidification Microstructure Evolution in Al Alloys After Laser Melting - Volume 22 Issue S3 - Jörg M.K. Wiezorek, Can Liu, Kai Zweiacker, Joseph T. McKeown, Thomas LaGrange, Bryan W. Reed, Geoffrey H. Campbell
Article
We present a new concept applicable to the epitaxial growth of dislocation-free semiconductor structures on a mismatched substrate with a thickness far exceeding the conventional critical thickness for plastic strain relaxation. This innovative concept is based on the out-of-equilibrium growth of compositionally graded alloys on deeply patterned su...
Article
Additive manufacturing (AM) of metals and alloys is becoming a pervasive technology in both research and industrial environments, though significant challenges remain before widespread implementation of AM can be realized. In situ investigations of rapid alloy solidification with high spatial and temporal resolutions can provide unique experimental...
Article
Full-text available
div class="title">Quantitative Determination of Thermal Fields and Transformation Rates in Rapidly Solidifying Aluminum by Numerical Modeling and In-situ TEM - Volume 21 Issue S3 - Can Liu, Kai Zweiacker, Joseph T. McKeown, Thomas LaGrange, Bryan W. Reed, Geoffrey H. Campbell, Jorg M.K. Wiezorek
Article
Full-text available
div class="title">Quantitative Phase Analysis of Rapid Solidification Products in Al-Cu Alloys by Automated Crystal Orientation Mapping in the TEM - Volume 21 Issue S3 - K. W. Zweiacker, M. A. Gordillo, C. Liu, J. T. McKeown, G. H. Campbell, T. LaGrange, B. W. Reed, J. M. Wiezorek
Article
In this study, the effects of Ultrasonic Nano-crystal Surface Modification (UNSM) on residual stresses, microstructure changes and mechanical properties of austenitic stainless steel 304 were investigated. The dynamic impacts induced by UNSM leads to surface nanocrystallization, martensite formation, and the generation of high magnitude of surface...
Article
The rapid solidification dynamics of a pulsed-laser-melted hypoeutectic Al–Cu thin-film alloy were monitored using in situ transmission electron microscopy with high spatial and temporal resolutions. Direct observation of the solid–liquid interface during the transformation allowed measurements of the time-evolving solidification front morphology a...

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